Which Wins: HTTPS, SPDY, or HTTP/2? A Real-World Performance Comparison

HTTP/2 promises clear performance gains, but the use of padding in response data introduces a potential trade‑off between speed and security.

Recent browser updates have made it possible to test these protocols: Firefox 35 ships with HTTP/2 support (draft 14) enabled by default, while Chrome requires manual activation via about://flags. HttpWatch now displays the protocol used for each request.

Performance Comparison

The tests were conducted with Firefox and HttpWatch on the Google UK homepage, switching between three protocols—original HTTPS, SPDY/3.1, and HTTP/2—by toggling settings in about:config. All tests used an empty cache.

Test #1: Request and Response Header Size

Most sites compress page content, but HTTP/1.1 cannot compress headers. SPDY uses the DEFLATE algorithm, while HTTP/2 employs the HPACK algorithm, which combines predefined tokens, a dynamic table, and Huffman coding.

Screenshot of header sizes (sent and received) shows HTTP/2 producing the smallest headers.

Winner: HTTP/2

Test #2: Response Size

Response size includes headers and the encoded body. Although HTTP/2 has the smallest headers, SPDY delivers a smaller overall response for text content because HTTP/2 adds optional padding bytes to data frames.

Images illustrate the larger response size for HTTP/2 due to padding.

Padding can obscure the true size of frames and mitigate attacks such as BREACH, but it is not applied to already‑compressed image files.

Winner: SPDY

Test #3: TCP Connections and SSL Handshake Time

Increasing the maximum concurrent connections per domain improves performance in HTTP/1.1. SPDY and HTTP/2 reduce the number of TCP and SSL handshakes by multiplexing multiple requests over a single connection.

Both protocols show lower handshake overhead compared with plain HTTPS.

Joint Winners: SPDY & HTTP/2

Test #4: Page Load Time

Page‑load time measured by HttpWatch reflects the moment the page is fully downloaded and usable. HTTP/2 consistently achieved the fastest load times, while HTTPS lagged due to lack of header compression and multiple connections.

Winner: HTTP/2

Conclusion

HTTP/2 appears to deliver noticeable performance advantages, yet the padding used in response data creates a nuanced trade‑off between speed and security.